Climate change could wipe out a third of parasite species. Yes, that would be a bad thing

Climate change could wipe out a third of all parasite species on Earth, according to the most comprehensive analysis to date.

Tapeworms, roundworms, ticks, lice and fleas are feared for the diseases they cause or carry, but scientists warn that they also play a vital role in ecosystems. Major extinctions among parasites could lead to unpredictable invasions of surviving parasites into new areas, affecting wildlife and humans and making a “significant contribution” to the sixth mass extinction already under way on Earth.

The new research, published in Science Advances, used the collection of 20 million parasites held at the Smithsonian Institution’s Museum of National History in the US to map the global distribution of 457 parasites. The scientists then applied a range of climate models and future scenarios and found that the average level of extinctions as habitats become unsuitable for parasites was 10 per cent by 2070, but extinctions rose to a third if the loss of host species was also included.

“It is a staggering number,” said Colin Carlson at the University of California, Berkeley, who led the new work. “Parasites seem like one of the most threatened groups on Earth.” The severity of the impact varied with the different climate scenarios. For example, a 20 per cent loss of parasite native ranges in scenarios where carbon emissions are rapidly cut in the future rises to 37 per cent if emissions continue unchecked.

“Parasites are obviously a hard sell,” said Carlson. “Even if you are grossed out by them – and there are obviously downsides for individual hosts and for humans – parasites play a huge role in ecosystems.” They provide up to 80 per cent of the food web links in ecosystems, he said. Having a wide range of parasites in an ecosystem also means they compete with one another, which can help slow down the spread of diseases.

“If parasites go extinct, we are looking at a potential massive destabilisation of ecosystems [which] could have huge unexpected consequences,” Carlson said, with other parasites moving in to take advantage. “That doesn’t necessarily work out well for anyone, wildlife or humans.”

One example of the complex role parasites can play is a hairworm that lives in grasshoppers in Japan and tends to lead its host to jump into water, where the grasshoppers become a major food source for rare fish. “In some subtle ways, parasites are puppeteers,” Carlson said.